1. Field of the Invention
The present invention relates to a method for manufacturing a substrate, in which metal columns of bumps press-fitted into an insulating resin layer provide connections between metal foils contact-bonded to a thermosetting insulating resin layer, or between a metal foil contact-bonded to a thermosetting insulating resin layer and an electrode of an electronic component built in the insulating resin layer, and more particularly relates to an improvement in reliability of an electrical connection.
2. Description of the Related Art
In general, double-sided wiring boards and multilayer wiring substrates are manufactured by connecting a wiring pattern of a metal foil on one principal surface of an insulating resin layer (organic resin layer) and a wiring pattern of a metal foil on the other principal surface thereof to each other through the use of metal columns penetrating through the insulating resin layer. In this case, when the metal columns are to be formed with the use of vias, the insulating resin layer requires the use of hole-forming processing, plating processing, etc., which make the manufacturing process complicated, and thus expensive, which is further also disadvantageous in that the component mounting density is limited.
Therefore, it has been proposed that this type of substrate is manufactured by press-fitting conductor bumps into an insulating resin layer from both principal surfaces of the insulating resin layer, and joining the tips of the bumps on the both principal surfaces so as to crush each other, thereby forming the metal columns (for example, see Japanese Patent No. 3474894 (paragraphs [0006] to [0017], FIG. 1, etc.)).
FIGS. 10A-10C schematically illustrate an example of a method for manufacturing a substrate as described in Japanese Patent No. 3474894, in which chevron bumps 200 of a conductive paste are formed on one side of a supporting base sheet 100 of a polyimide resin film (FIG. 10A). In addition, a thermoplastic polyetherimide resin film is prepared as a synthetic resin sheet (insulating resin layer) 300. Then, the three layers of the supporting base sheet 100 with the conductive bumps 200, the synthetic resin sheet 300, and the other supporting base sheet 100 with the conductive bumps 200 are stacked to form a laminated body, in such a way that the conductive bumps 200 are opposed to each other. Furthermore, a polyimide resin film of the same type as the supporting sheet 100 or aluminum foil is stacked and placed as a backing plate 400 on the other sides opposite to the bump formation sides of the stacked supporting sheets 100 (FIG. 10B), and the backing plates 400 are placed between hot plates for hot pressing, which backing plates 400 are kept at 120° C. and arranged to keep the synthetic resin sheet 300 thermoplastic under pressure, and cooled to separate the sheets 100 and 400, thereby forming a final substrate 500. The substrate 500 has, as shown in FIG. 10C, metal columns 600 formed as the connecting conductors, which are obtained by electrically connecting the bumps 200 in physical contact with each other, in such a way that the conductive bumps 200 on the both principal surfaces of the synthetic resin sheet 300 are press-fitted into the synthetic resin sheet 300 to crush the tips of the bumps 200 on both sides, and undergo plastic deformation. The both end surfaces of the metal columns 600 are joined to, for example, wiring patterns of metal foil formed by printing or the like on the both principal surfaces of the synthetic resin sheet 300, thereby manufacturing a printed wiring board (substrate) 500 with the metal columns 600 forming the connecting conductors to penetrate through the synthetic resin sheet 300.
In the case of the method for manufacturing a substrate as described in Japanese Patent No. 3474894, the metal columns 600 penetrating through the synthetic resin sheet 300 are formed in such a way that the bumps 200 on the both principal surfaces, which are press-fitted into the synthetic resin sheet 300, have tips crushed to each other to undergo plastic deformation, thereby only forming electrically connecting conductors in physical contact. Therefore, the metal columns 600 lack reliability as an electrically connecting conductor, and have the problem of being unable to improve the reliability of the electrical connection between both principal surfaces of the synthetic resin sheet 300.
Thus, in the field of manufacturing substrates such as double-sided wiring boards and multilayer wiring substrates, it has been desired to manufacture a substrate with improved reliability of an electrical connection between metal foils on both principal surfaces of an insulating resin layer by a simple and inexpensive approach which requires no hole-forming processing or plating processing for the insulating resin layer unlike the synthetic resin sheet 300. Furthermore, in the field of manufacturing built-in component substrates with electronic components such as capacitors, coils, and transistors built in an insulating resin layer such as the synthetic resin sheet 300, it has been also desired to improve the reliability of an electrical connection between a wiring pattern of a metal foil and electrodes (external electrodes) of the electronic components by a simple and inexpensive approach.